The present invention relates to a method for the digital transmission of information in short-wave radio networks having a plurality of stations with a transmitter and/or a receiver, in which, for the purpose of channel condition estimation at the receiver end, a reference signal is added to and is transmitted with the data signal containing the actual information.
Channels such as those of the short-wave, a priori those having an unknown phase angle, conventionally use non-coherent receiver detectors, for example frequency shift keying FSK or on/off keying OOK. If the fading can be designated as slow relative to the signal element duration, that is if the coherence time is considerably longer than one signal element, then a substantial gain can be obtained by utilizing the process memory. In this case a partial coherent detection is used in conjunction with a phase estimation from the receive signal, which is described for example in the book "Detection, Estimation and Modulation Theory", Part I, by H. L. Van Trees, Wiley and Sons, New York 1968.
By means of the invention, these methods known hitherto only from theory are now to be improved and extended to the extent that they can be used to meet the special requirements of the short-wave transmission. These requirements are in particular extremely low signal-to-noise ratio (SNR) and signal interference ratio (SIR), fading, slightly drifting local oscillators and time bases, high noise burst frequency and influencing by the receiver AGC (AGC=automatic gain control).